It is the technique by which investor expects that the value of an asset will decrease for a short duration, perhaps in the next few weeks. In this process, the investor borrows the shares from the investment company to sell to another investor. Companies have a large number of shares on hand or borrow from other company to provide loan to an investor. However, an investor returns the shares they borrow. The main intent is to sell the stock at a higher price then buy them back at a lower price.
Long and short positions are exactly opposite to each other. If an investor has opted for a long position, it means that an investor has owns the shares of stock. By contrast, if the investor owes the stocks to someone but not as the owner of the stock, it is considered a short position. In the case of options, holding or buying a put or call option is a long position, the investor has the right to buy or sell to the specified person at a certain price. Conversely, writing a call or selling or put option is considered as a short position where the writer must sell or buy from the long holder or buyer of a certain option.